The Battle of Passchendaele, at which Jacob commanded II Corps, during the First World War

In 1894, he married Clara Pauline Wyatt, daughter of the Reverend J. L. Wyatt, well known as a missionary and student of oriental languages in India, and also a lecturer in Tamil at Cambridge University from 1895 to 1929. The couple had one son, Edward Ian Claud Jacob, who later became Assistant Military Secretary of the War Cabinet and Director-General of the BBC.[31]